What does "all the words of Hashem ... " come to include?
Ramban #1: Moshe related to Aharon the entire contents of his communication with Hashem - including his refusal to undertake the Sh'lichus and that ultimately, he had was sent against his will.
Ramban: (citing Midrash Chazis): He taught him the Names of Hashem. 1
As discussed earlier (See 3:14-15).